The invention can be applied advantageously for rendering smart cards secure, especially the smart cards used in encrypted television.
Generally speaking, smarts cards comprise a plastic card body and an electronic module inserted in a cavity fitted in said card body. The electronic module is made up of an integrated circuit or chip placed on a support provided with metallic zones for ensuring the electric link between the module and a card reader. The integrated circuit can be an EEPROM type memory for, for example, telecard applications or a microprocessor for bank card, mobile `phone or even encrypted television applications.
Thus, most of the smart cards are used to carry out electronic transactions, which naturally implies that there is an attempt to defraud those systems using smart cards so as to be able to benefit from the services provided by these systems without paying for said services.
So as to avoid or, at least, limit the fraud, the information exchanged with the smart card electronic module are encrypted according to various well-documented methods. It merely suffices to be aware that the messages received by the integrated circuits of the cards are encrypted with keys known an encrypting keys and are stored in the non-volatile memory of the circuits. These keys can be protected against any external reading by masking the level of the memory plane in which they are recorded by several levels of metal serving as a screen whilst taking part in the dynamics of the circuit.
However, the degree of safety obtained is not absolute as it is always possible for an experienced defrauder to gain access to the secret keys via a functional analysis of the integrated circuit.